In recent years, the number of subscribers to mobile communication services has exceeded five billion and is growing quickly. Mobile communication technologies have been developed to attempt to satisfy the increasing demand and to provide more and better mobile communication applications and services. As more people use mobile communication systems and more services are provided over these systems, there is an increasing need for mobile communication systems with larger capacity, higher throughput, lower latency, and better reliability.
Conventionally, millimeter waves refer to radio waves with wavelength in the range of 1 mm to 10 mm, which correspond to radio frequencies of 30 GHz to 300 GHz. These radio waves exhibit unique propagation characteristics. For example, compared with lower frequency radio waves, they suffer higher propagation loss, have poorer ability to penetrate objects, such as buildings, walls, foliage, and are more susceptible to atmosphere absorption, deflection and diffraction due to particles (e.g., rain drops) in the air. On the other hand, because of their smaller wave lengths, more antennas placed into a relative small area, thus enabling high-gain antenna in a small form factor. In addition, due to the aforementioned deemed disadvantages, these radio waves have been less utilized than lower frequency radio waves. Additionally, higher frequencies in the super high frequency (SHF) band (e.g., 3 GHz to 30 GHz) also exhibit similar behavior as radio waves in the extremely high frequency (EHF) band (i.e., millimeter waves), such as large propagation loss and the possibility of implementing high-gain antennas in small form factors.
Vast amount of spectrum are available in the millimeter wave band. For example, the frequencies around 60 GHz, which are typically referred to as 60 GHz band, are available as unlicensed spectrum in most of the countries. Recently, many engineering and business efforts have been invested to utilize the millimeter waves for short-range wireless communication.
Therefore, there is a need for improved wireless communication systems and, more specifically, to reporting channel quality information for beams used in a wireless communication system.